1. Technical Field
The present invention relates to a method for producing a sintered body and a sintered body.
2. Related Art
A metallic sintered body is typically produced by forming raw powder (mixed powder), i.e., a mixture of metal powder and a binder, into a green body by use of various kinds of forming methods such as an injection molding method or the like, debinding the green body at a temperature higher than a melting point of the binder but lower than a sintering point of the metal powder to thereby obtain a brown body, and sintering the brown body thus obtained.
In the meantime, the raw powder used in, e.g., an injection molding method, contains a binder in a relatively large quantity in order to improve flowability during the injection molding process. Therefore, a heating operation needs to be performed for an extended period of time to remove the binder. This poses a problem in that the production efficiency of a sintered body is lowered and deformation occurs in a green body during the heating operation.
Furthermore, it is impossible for the heating operation to completely remove the binder contained in the green body. This poses another problem in that vaporization of a residual binder in a sintering process creates cracks in the sintered body.
In an effort to solve these problems, there has been disclosed a method for producing a brown body which is obtained by heating a green body constituted of a raw powder being a mixture of metal powder and a binder containing polyacetal in a gaseous acid-contain atmosphere or a boron trifluoride contain atmosphere (see, e.g., Japanese Patent No. 3,128,130).
In general, acid is one of deleterious substances, and boron trifluoride is one of poisonous substance and therefore is detrimental to a human body. For this reason, the task of handling acid involves a great deal of toil, which is partly attributable to the necessity of using a heavy protection device.
Moreover, acid and boron trifluoride have a strong property of dissolving metal. This requires use of a highly corrosion-resistant material in the equipments for production of a metal brown body, which makes the metal brown body costly to produce.
In addition, acid becomes a cause of air pollution when it is discharged to the air at the end of a heating operation. This means that there is a need to prevent acid from being discharged to the air. However, it is costly to prevent the discharge of acid to the air.